Fine particles, microcapsules, granules, tablets, and the like, comprising useful coated substances in a variety of forms or with various properties, such as colorless or colored dyes, pharmaceutical products, agrochemicals, fragrances, flavors, and savories, feed materials, and food product materials, have conventionally been prepared for industrial purposes. Known examples of bases for coating fragrances, flavors, and savories, feed materials, food product materials, and the like, specifically, coating agents, include waxes and other oils, natural polysaccharides, proteins, shellac (natural resin secreted by the lac insect living in plants such as the legumes) and other resins, and the like. Chemically synthesized coating bases stipulated for pharmaceutical additives are also known in the case of pharmaceutical products. As for packaging films, chemical products such as nylon, PVDC, aluminum-deposited films, are mainly used, and with regard to natural products, only a slight amount of pullulan is produced.
Most of such conventionally known coating agents, however, suffer from the drawback of poor handling as a result of stickiness or poor dispersion during the preparation of the coating liquid. Additional problems with most pharmaceutical additives such as shellac, zein (corn protein), and ethyl cellulose, which are their bad effects on the environment and their high cost because of the use of solvents such as ethanol have been indicated. Although water dispersion types of ethylcellulose-based coating agents have become commercially available recently, these also suffer from problems in terms of handling, such as the changes in solution properties depending on temperature conditions during storage, and the inability to release them in wastewater into rivers because they contain various solvents. Still another problem is the poor dissolution in intestines and the extremely slow dissolution speed of the aforementioned zein which can be used in the field of food products.
In addition, based on the recent environmental issues, manufacturers substitute aluminum-deposited films, etc. for PVDC, which is excellent in both oxygen- and vapor-barrier properties, for fear of emission of dioxin. However, there arises a move for further cost reduction, improving the usefulness, images and environment-consciousness. As part of the move, manufacturers are cornered into a situation wherein they must advance the applied researches of biodegradable plastics and edible films.
Attempts have meanwhile been made to develop film materials from yeast. Japanese Patent Publication No. 56-19971, for example, discloses an edible protein film based on water-soluble proteins produced by removing the yeast cell membrane components from residual yeast which was produced by extracting nucleic acid. Japanese Laid-Open Patent Application No. 53-45385 discloses a method for producing a film, wherein the cells of a microorganism such as yeast are heated and alkali treated, acid is added for treatment involving isoelectric precipitation, the pH of the resulting precipitate is adjusted to between 6 and 8, and a plasticizer is added to the resulting gel-forming microorganism cells to produce a constituent.
Further, Japanese Laid-Open Patent Application No. 2000-44878 describes: a coating agent whose primary component comprises yeast cell wall fractions consisting of cell residue obtained by removing the internal soluble cell components of enzyme-treated yeast; a coating agent whose primary component comprises acid-treated yeast cell wall fractions consisting of cell residue obtained by removing the internal soluble cell components of enzyme-treated yeast, the aforementioned residue being treated with an acidic aqueous solution to further remove solubilized components; the aforementioned coating agents which comprise a plasticizer. These are thought to be coating agents with an extremely low oxygen permeability coefficient, which remedy the drawbacks of the conventional edible coating agents mentioned above, for example, by having a finish that is not as sticky, despite its viscosity, as gums such as gum arabic, resins such as shellac, and zein or Eudragit, and which results in coated particles and/or granules that do not stick to each other, as well as to be an excellent coating agent which can be used as an enteric coating agent capable of controlling the time at which dissolution begins.
As aforementioned, the completeness of the coating agent described in Japanese Laid-Open Patent Application No. 2000-44878 is extremely high, however, it has been found that in case where a film is manufactured with the use of the above-described coating agent whose primary component comprises yeast cell wall fractions, or a coating agent wherein glycerin as a plasticizer is added to the yeast cell wall fractions, the film fully displays its oxygen-barrier property under low humidity of RH 0%, while the value increases about 60-fold under high humidity of RH 60%. The object of the present invention is to provide a coating agent which is applicable even in 100% water, which affords a finish that is not sticky despite its viscosity, thus resulting in coated particles and/or granules that do not stick to each other, a coating agent having a function to control dissolution time, coated materials comprising the use of such coating agents, a film formed from such a coating agent, which has an extremely low oxygen permeability coefficient even under highly humid conditions, packaging materials comprising the film, and packaged items packaged with the packaging materials.